The polarization conversion from optical orientation to alignment in single InAlAs/AlGaAs quantum dots (QDs) was studied in detail under zero and nonzero magnetic fields. Under the influence of the effective magnetic field, bright exciton doublets precess in pseudospin space, where the torque vector is composed of the external magnetic field and the anisotropic exchange field. For a number of QDs, we measured the angle difference of the polarization axes obtained with circularly polarized excitations, which is an indicator of the conversion efficiency under a zero magnetic field. By applying a longitudinal magnetic field, a high conversion efficiency of ∼50% was achieved. Additionally, the exciton spin-relaxation time and the magnitude of built-in linear dichroism were estimated from the exciton spin dynamics using the three-dimensional pseudospin precession model, and a long spin-relaxation time exceeding the recombination lifetime was obtained. Finally, we discussed the influence of a nuclear magnetic field on the polarization conversion.
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